T'au is the homeworld of the Tau species in the star system of the same name and the largest and most politically important Sept of the Tau Empire. The High Council, led by Ethereal Supreme Aun'Va, convenes here, its decrees shaping the entire empire. Even after the growth of the Tau Empire into an interstellar civilization, T'au remains the centre of Tau culture and bureaucracy. No other Sept world can challenge the prestige of T'au, and only Vior'la can match it's power.
T'au was discovered and categorised by the Adeptus Mechanicus' Explorator vessel Land's Vision a few thousand standard years before the emergence of the Tau as a space-faring race in the 39th Millennium. Before the Imperium of Man could cleanse the planet of the then-primitive Tau population, a freak Warp Storm occurred and effectively sealed the planet and the surrounding region off from contact with the rest of the galaxy. In the few thousand standard years since, the Tau underwent very rapid technological evolution, emerging as a highly technologically advanced starfaring race just as the Warp Storm dissipated in the 39th Millennium. T'au is a warm, dry and arid world. Preference for worlds with climates like that of T'au drives Tau colonization towards certain planets and away from others.
- Codex: Tau (3rd Edition)
- Codex: Tau Empire (4th Edition)
- Codex: Tau Empire (6th Edition), pg. 28